1. Field of the Invention
The present invention relates to a magneto-resistive effect (MR) element, magnetic head, magnetic head slider, head gimbal assembly and hard disk drive apparatus. In particular, the present invention relates to a configuration of a spacer layer and a cover layer of a stack.
2. Description of the Related Art
Reproducing heads with high sensitivity and high output are in demand in conjunction with condensing of high recording density in hard disk drives (HDD). As an example of this type of reproducing head, a spin valve head has been developed. A spin valve head includes a nonmagnetic metal layer and a pair of ferromagnetic layers positioned on both sides of the nonmagnetic metal layer in a manner of contacting the nonmagnetic metal layer. The magnetization direction of one side of the ferromagnetic layers is pinned in one direction (hereinafter, this type of layer is referred to as a magnetization pinned layer), and the magnetization direction of the other side of the ferromagnetic layers freely rotates in response to an external magnetic field (hereinafter, this type of layer is referred to as a magnetization free layer). When an external magnetic field is applied, the relative angle of the spins between the magnetization pinned layer and the magnetization free layer changes so that magneto-resistive change is realized. Typically, the magnetization direction of the magnetization pinned layer is pinned by utilizing the exchange coupling force of an anti-ferromagnetic layer.
On the other hand, in order to realize further condensing of high recording density, a reduction of a read gap (a space between upper and lower shield layers) is required. However, when the read gap is reduced to about 20 nm, placing an anti-ferromagnetic layer within the read gap becomes difficult. Therefore, a configuration has been developed in which a pair of magnetization free layers is arranged on both sides of a spacer layer. According to this configuration, reduction of the read gap is easily realized because an anti-ferromagnetic layer is unnecessary.
With either configuration, the spacer layer is a necessary component to realize magneto-resistive change, and promising spacer layer materials have been developed to achieve a large magneto-resistive ratio (hereinafter referred to as the MR ratio). On the other hand, the layers such as the spacer layer, magnetization pinned layer, magnetization free layer, etc. are processed into extremely fine shapes to accurately detect a magnetic field emitted from a specified bit of a magnetic recording medium. Specifically, after film formation, these layers are processed into a pillar or trapezoidal stack, and a bias magnetic field application layer that applies a bias magnetic field to the periphery of the stack is arranged. In particular, since the bias magnetic field application layer is conductive, the periphery of the stack is covered by an insulative cover layer to prevent a sense current from leaking in the bias magnetic field application layer. As described above, the cover layer is disposed for a purpose of maintaining an insulation property on side surfaces of the stack, and conventionally, Al2O3 has been typically utilized. However, the cover layer directly contacts the spacer layer as well as the magnetization pinned layer and the magnetization free layer, and the effects on the MR ratio, etc. are noted. Therefore, various technologies regarding combinations of the spacer layer and the cover layer are disclosed.
U.S. Patent Application Publication No. 2009/0059443 discloses a spacer layer where a semiconductor layer composed of either ZnO, In2O3 or SnO2 is sandwiched by metal layers composed of Cu, Au, etc. The cover layer is configured with two layers. An inner layer contacting the stack is composed of HfO2, MgO, ZrO2, Ta2O5, TiO2, etc; and an outer layer is formed with an insulating layer composed of Al2O3, SiO2, etc.
U.S. Patent Application Publication No. 2009/0067099 discloses materials for the spacer layer that are similar to U.S. Patent Application Publication No. 2009/0059443, and discloses a cover layer with a three layer configuration also. An innermost layer of the cover layer is formed of a material in common with the spacer layer, and, for example, ZnO is disclosed. A middle layer is disposed for a purpose of forming a Schottky barrier at an interface with the innermost layer, and is formed of Os, Ir, Pt, etc. An outermost layer is formed with an insulating layer made of Al2O3, SiO2, etc.
It is an object of the present invention to provide an MR element that can realize a large MR ratio by further improving a configuration of a spacer layer and a cover layer.